'Everyone grab a giant boob!' someone shouts. And they mean it in the best possible way.

It's 8am on a brisk Wednesday morning, and 100 nimble-footed participants have gathered in central London to take part in a giant 'flashmob' - a sudden choreographed dance routine set to music, aimed at surprising passers-by - and we're all getting dressed up as enormous breasts.

The event has been organised by breast cancer awareness charity CoppaFeel!, the organisation founded by 26-year-old identical twins Kris and Maren Hallenga, whose lives were turned upside down in 2009.

Kris and Maren Hallenga, centre front right and left, stand either side of choreographer Zoe Jackson, founder of Living The Dream, to lead the CoppaFeel! flashmob troupe in St Christopher's Place

That year, when the girls were just 23, Kris was diagnosed with breast cancer - a horrifying eight months after first going to her GP with concerns about lumps she was finding in her painful chest.

Dismissed as 'hormones' and told she was far too young to have the disease, the cancer went undiagnosed for so long that it spread to her spine, only finally diagnosed when the twins' no-nonsense mother marched Kris to the doctor and demanded to be taken seriously.

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Kris now has stage four cancer, explaining that 'you can't go back a stage, and there is no stage five.'

Despite all this, Kris is 'living with cancer' and doing OK. She still has treatment, but so far it's all going well.

(What's more, her work has not gone unnoticed. She carried the Olympic torch through Tower Hamlets on 21 July, she's been given a Pride of Britain award, she's attended a Downing Street reception and was shortlisted for the Women of the Future Awards in 2011.)

Zoe Jackson, centre front, choreographer and founder of Living The Dream, leads the CoppaFeel! flashmob in London's West End this morning

And on this crisp October morning
just off Oxford Street, she and her sister are virtually indistinguishable: two gorgeous leggy blondes who
both look the picture of glowing health.

(In fact, the only way many of us are able to tell them apart is by Kris's jazzy leggings.)

But both Kris and Maren are insistent that no
more young women get such a rude awakening as theirs, and so here we are, on St
Christopher's Place, during Breast Cancer Awareness Month, determined to bring attention to CoppaFeel!, with
inflatable breasts strapped to our fronts.

Kris, left, and Maren Hallenga, right, and their enormous breasts receive some admiring glances on St Christopher's Place

All 100 participants (me included) have
been given an online link to a video of the routine which was put
together by choreographer extraordinaire - and friend of the Hallengas Zoe
Jackson - founder of Living The Dreamperforming arts company, and winner of 2011 Women of the Future Award in the arts category.

So we've all had time to practice and there is no excuse for putting a foot wrong.

(That said, any neighbours who witnessed me clod-hopping around my sitting room at 5am this morning to James Brown's I Feel Good and Turn On, Tune In, Cop Out by Freak Power would probably attest to the fact that I still needed much, much, much more practice.)

Zoe Jackson and her giant inflatable breast, centre, lead the others through the routine to the delight of passers-by

After a quick run-through, we're ready to go, positioned around the various mews entrances onto St Christopher's Place, which is itself marking Breast Cancer Awareness Month by getting 'pink'd', adorning the streets with pink bunting and running a number of themed events.

By now it's just before 9am, and the rush hour crowd is making its way to work, pausing to see what in the name of inflatable breasts is going on. The camera phones are coming out. We can hear the giggles over our nervous heartbeats.

The music kicks in and the first gang of bouncing breasts run out, high-kicking, clapping, twisting, turning, rolling, jumping, leaping, grinning and, on occasion, whooping.

Right on cue (My Humps by the Black-Eyed Peas; are you sensing a theme to the aural selections yet?), the second batch of breasts make a beeline for the front, pointing at their inflatable friends when Fergie hollers 'check it out!'.

'Checking it out' is, after all, the point of our flashmob and the modus operandi of CoppaFeel!.

Kris didn't check her breasts until it was too late. Now she and Maren want us all - both women and men, for the disease can attack men, too - to cop a feel of ours.

'The charity is particularly about getting young people to check their boobs,' Kris, told MailOnline. 'I thought I was too young to get breast cancer and that it would never happen to me. I was wrong. Young people need to become familiar with their breasts so they can sense when something changes.'

But there's no time for breast-checking just now in St Christopher's Place: right now it's time for me and my fellow breasts to bolt out of our starting blocks and into the melee.

Three dancers run out to join the CoppaFeel! flashmob

It all comes together and looks amazing - at least from where I'm standing at the back of this sea of breasts.

'We like doing fun things like this,' said Kris, who prefers the term Boob Chief to CEO when it comes to her charity. 'The whole point of Coppafeel! is that
we go about awareness in different and engaging ways. We like causing a bit of a stir.

'We use these inflatable boobs stuffed with balloons for publicity events. The last thing we did was the BoobTube where 50 people from AOL wore them on the underground during rush hour. And people use them to run half marathons.

'We have a big cinema advert coming out soon which is terrific because the more people who are aware of us and aware of the importance of checking your boobs the better.

'The giant inflatable boobs really cause an impact which is why we like them. We have them made in different shades by a man in China - It's funny because I don't know if he has any idea what we use them for!'

For more information and to sign up for breast-checking reminders, visit the CoppaFeel! website. You can read Kris' blog here. For more information about St Christopher's Place GET PINK'D campaign and the events taking place there this month, visit their website.